This invention relates to the production of premium lubricating base oils from shale oils.
Methods of recovering a raw shale oil from oil shale are well known, and as with petroleum crudes, a raw shale oil (sometimes called a syncrude) must be upgraded to products which are of commercial utility. For example, in U.S. Pat. No. 4,428,862, a method is taught for successively deashing, dearseniting, hydrotreating and hydrodewaxing a raw shale oil so as to produce a "pipelineable" shale oil having a relatively low pour point (i.e., +30.degree. F. or less). Such pipelineable shale oils are disclosed to contain various jet fuel and diesel fuel fractions meeting appropriate commercial freeze point and pour point requirements.
Another product of commercial interest is lubricating base oil. Lubricating base oils are generally categorized by their boiling point range, as shown in the following table:
TABLE I ______________________________________ Typical Lubricating Base Boiling Point Oil Designation Range, .degree.F. ______________________________________ Light Neutral 650 to 825 Medium Neutral 700 to 925 Heavy Neutral 800 to 1025 Bright Stock 1000+ ______________________________________
Commercially acceptable lubricating oils generally are composed of blends of base oils having a pour point no greater than +10.degree. F. while also having viscosity indices typically between 90 and 100. Viscosity index is a measure of how well a lubricating oil maintains its viscosity as a function of temperature, with ever increasing viscosity index values being indicative of oils which better maintain their viscosity with change in temperature. For most lubricating oils, a desired viscosity index is 95 or higher.
Yet another product of commercial interest is transformer oil, which typically boils in the range of 610.degree. to 650.degree. F. For transformer oils, there is no viscosity index requirement, since temperature fluctuations in transformer service are minimal. However, there are stringent pour point requirements. Transformer oils are required to have a pour point no greater than -40.degree. F.